Home > Storage > PowerScale (Isilon) > Product Documentation > Storage (general) > PowerScale OneFS SmartFlash > Introduction to OneFS cache coherency
The OneFS caching subsystem is coherent across the cluster. If the same content exists in the private caches of multiple nodes, this cached data is consistent across all instances. For example, consider the following initial state and sequence of events:
OneFS uses the MESI protocol to maintain cache coherency. This protocol implements an “invalidate-on-write” policy to ensure that all data is consistent across the entire shared cache. The following diagram illustrates the various states that in-cache data can take, and the transitions between them. The various states in the figure are: